Review of Successful Tree and Shrub Planting

We do a great job of killing trees we obviously intended to serve a purpose in the landscape, so I want to review the most important cultural practices that impact survivability of newly planted trees (and shrubs).

Right plant—right place

There are two basic steps, no matter what tree is going to be planted. The first is to have a soil test done—Penn State does a baseline test for $10.00. This is especially important if it is a new planting area for the desired plant(s), or the area is being converted from turf to a landscape bed. Remember the saying "Right plant, right place?" If the soil pH is too high or too low for the desired plant, it will not grow normally. If the soil is lacking a major or micro-nutrient, the plant will not grow properly.

The second basic step is linked to the soil test and continues the "right plant, right place" practice. The site has to meet the sunlight requirements of the plant and, there has to be enough horizontal and vertical space for the tree or shrub to grow. Make sure you do your research so you know the dimensions of the mature tree or shrub.

The importance of the actual planting steps

There are two components of successfully digging a planting hole – the depth and the width.

Depth

The proper depth of the planting hole for either a field dug (balled and burlapped) or container grown plant should be the depth of the root mass. The top of the root ball should be slightly above the soil grade. The root flare should be visible and used as a guide for setting the correct depth. The root flare is where the large structural roots extend out from the trunk. By far, the most common mistake of the planting process that I encounter is woody plants planted too deep. The planting hole depth is too great, and usually in combination with excess soil having been placed on top of the root ball during the digging process. This excess soil needs to be removed first to set the depth correctly. This is where the root flare serves as the guide for finding the top of the original root ball. Planting too deep submerges the root mass so that oxygen availability is reduced. Also, the trunk's bark is a defensive structure. When soil (and mulch) is piled against it, the bark is kept wet, and it becomes easier for pathogens or insects to compromise.

Width

The width of the planting hole should be at minimum twice as wide as the root ball. In a perfect world, it can be much wider. The reason for this is that it is easier for the plant to establish a new root system in the backfill soil, which will have larger pore space due to the disturbance caused by digging. If you dig a cylinder-shaped planting hole with smooth sides, the fine feeder roots will struggle to spread out from the original planting hole because they encounter only micro-pores. The lack of an extensive root system stunts the plant's growth and can lead to its decline.

Setting a container-grown tree

Now that the planting hole has been properly dug, the plant can be set in for permanent placement. If it is a container-grown plant, the container needs to be removed. You would think that would be obvious, but I have seen plants planted while still in the container, and people want to know why they died! Observe the roots of container-grown plants. Is the root system composed primarily of white, fine roots, or is it a jumble of thicker, bark-covered ones? You want the first one. The roots should also be cut/ripped apart with a shovel or soil knife so that new growth spreads laterally in the soil. If this isn't done, the root system will primarily stay in the "container shape" and not develop an extensive network that is required to sustain the plant.

Setting a balled/burlapped tree

If you have selected a balled and burlapped tree, the root system will have already been cut, so you are not going to have to break it apart. What you do need to do is remove as much of the "stuff" that's around the root ball as possible. This includes the wire basket, the burlap, the twine and anything else that you may find. Do not leave this material on and then backfill the hole with soil. All of these can girdle (strangle) structural roots and the base of the tree. I have encountered so many trees that have been killed because the twine was not removed, and eventually cut through the cambium layer around the circumference of the trunk. This typically shows up years after planting. At this time, you can also check the base of the tree for any "J-shaped" roots. These are roots that bend and are not perpendicular to the trunk. At some point in the future, the curving root and trunk meet, and the root compresses the trunk and causes problems in the canopy.

The trees and shrubs planted for your customers will provide many years of pleasure—hopefully for generations. We need to review the basics while planting to give them the best opportunity to do so.

Removing excess soil and girdling roots. Photo: Tim Abbey, Penn State